Material used for spring connection devices must exhibit the ability to maintain adequate contact pressure for the design life of any part formed from the material. This ability to maintain adequate contact pressure is the ability to resist stress relaxation over a period of time, especially at temperatures elevated above normal room temperature. The current trend in connector design has been to place greater emphasis upon the maintenance of high contact pressure on connector parts at mildly elevated temperatures to reduce problems which might develop as the service temperature of the parts increases. Alloy 260 is currently widely used for electrical connectors but tends to exhibit a rather poor stress relaxation resistance at temperatures of 75.degree. C. or higher. Accordingly, it is important that this widely used alloy be modified in such a manner so as to improve its elevated temperature stress relaxation performance.
It is important to any modifications of Alloy 260 that high conductivity alloy be maintained along with improved stress relaxation performance. Furthermore, bend formability should be maintained while any cost increase in the alloy should be held down as low as possible to keep such an alloy competitive in the market. Other performance characteristics such as stress corrosion, solderability, softening resistance and others should not be significantly degraded below those properties shown by Commercial Alloy 260. It is desirable to the present invention that the performance of such an alloy exhibit approximately a 10-30% increase over projected stress remaining after 100,000 hours at 75.degree. C. or higher relative to Alloy 260. It is also desirable in the present invention that such an alloy maintain approximately a 20% IACS conductivity.
One alloy system which has been developed in the prior art is an improved beta-brass alloy as shown in U.S. Pat. No. 4,055,445 to Horace Pops. This particular patent teaches a brass alloy which exhibits a shape memory effect and which may contain from 25 to 40% by weight zinc along with 0.25 to 3.0% by weight silicon. It should be noted that the only useful alloy system within this broad range is shown by the cross hatched area in FIG. 3 of said patent, wherein the alloy should have a minimum amount of 25% by weight beta-phase up to 75%. Apparently, not only the particular alloy system itself but its specific processing is important in preparing the improved alloy of this particular patent. It is quite important to this patent that an annealing be performed so as to provide the above-mentioned minimum amount of beta-phase material within the alloy system.
It is a principal object of the present invention to provide an alloy system which exhibits improved stress relaxation resistance, particularly at elevated temperatures, when compared to Commercial Alloy 260.
It is a further object of the present invention to provide an alloy system as aforesaid which exhibits improved stress relaxation resistance and maintains approximate conductivity values found in Alloy 260.
It is an additional object of the present invention to provide an alloy system as aforesaid which is essentially an all alpha-phase alloy with up to 10% beta-phase within the alloy.
It is an additional object of the present invention to provide an alloy system as aforesaid which provides the noted benefits without appreciably increasing the cost of such an alloy.
Further objects and advantages will become apparent from a consideration of the following specification.